The present invention relates to an electronic lock system and, in particular, it concerns an electronic lock system which can also be manually operated.
It is known to provide electronic locks of various kinds. Such locks may generally be viewed as being made up of three parts: an authorization module for selectively allowing activation of the lock by certain keys or personnel; an electromechanical actuation system for generating the required mechanical movement of the lock mechanism; and a control system for controlling the functions performed by the actuation system in response to authorized activation of the lock.
One example of an electronic lock system may be found in U.S. Pat. No. 4,972,182. As is typical of existing electronic lock systems, the actuation system employs an electric motor which operates with a high gear ratio, in this case through a worm gear drive, to drive the lock mechanism.
A shortcoming of such actuation systems lies in implementation of a mechanical override. This is a vital safety feature, allowing opening of the lock during electrical failures and the like, and should preferably be easily and rapidly operable. However, in any system with a high gear transmission between the motor and the lock mechanism, the gear system acts as a lock preventing direct turning of the lock mechanism itself. Instead, the prior art provides a manual input to the motor side of the gears, requiring a large number of turns to open the lock mechanism.
In an attempt to achieve a more rapidly operable manual control, some commercial products have attempted to provide a clutch arrangement to disconnect the gears for manual operation. Besides being complicated and expensive, such arrangements are also mechanically unreliable under the normal working conditions of a door which include repeated mechanical impacts and thermal deformations.
A further shortcoming of conventional electronic lock systems with manual override is that, when the lock mechanism has been manually turned, the lock cylinder may be left in an intermediate position in which operation of a mechanical key is impossible.
There is therefore a need for an electronic lock system of simple and cheap construction which provides for easy and rapid manual operation. It would also be advantageous to provide a robust electronic lock system which deactivates itself when the lock is obstructed and which automatically corrects any problems of misalignment.